This disclosure relates to a method for increasing thermal and/or electrical conductivity of polymers through a multi-layering process, and more specifically for increasing thermal and/or electrical conductivity of shape memory polymers.
Shape memory polymers (SMP) are known in the art and generally refer to a group of polymeric materials that demonstrate the ability to return to some previously defined shape when subjected to an appropriate thermal stimulus. Shape memory polymers are capable of undergoing phase transitions in which their shape orientation is altered as a function of temperature. Generally, SMP have two main segments, a hard segment and a soft segment. The previously defined or permanent shape can be set by melting or processing the polymer at a temperature higher than the highest thermal transition followed by cooling below that thermal transition temperature. The highest thermal transition is usually the glass transition temperature (Tg) or melting point of the hard segment. A temporary shape can be set by heating the material to a temperature higher than the Tg or the transition temperature of the soft segment, but lower than the Tg or melting point of the hard segment. The temporary shape is set while processing the material at the transition temperature of the soft segment followed by cooling to fix the shape. The material can be reverted back to the permanent shape by heating the material above the transition temperature of the soft segment. Shape recovery can be set at any temperature between −63° C. and 120° C. or above. By changing the structure and composition of the polymer, the transition temperatures and mechanical properties of the SMP can be optimized for a particular application.
Addition of thermally and/or electrically conductive fillers to polymer matrices is known. The conductive fillers may be particulate or fibrous, and may be made from a variety of materials such as metals, metal alloys, and conductive carbon black. Generally, unfilled polymers are electrical and thermal insulators. By adding conductive fillers, heat dissipation can be improved by increasing the thermal conductivity of the blend. Addition of electrically conductive fillers allows conducting paths through the polymer blend, thereby lowering the resistivity of the polymer.
Microlayer extrusion to form multilayered components is known. For example, WO 01/21688 to Pulford et al. generally discloses the use of a duplex extruder with multilayering dies to produce a multilayered rubber component.